Effects of phase separation in crosslinked resins containing polymeric modifiers
The study reported in this thesis concerns the relationship between morphology and the properties of multicomponent epoxy and methacrylate resins. The thermodynamic and kinetic aspects of phase separation in reactive, thermosetting, systems are explored and applied to the investigation of blends of 'high performance' epoxy resins with polyethersulphone. The mechanical properties of the same cured blends are shown to be insensitive to considerable variations in composition, cure and the resulting morphology, both in the bulk-resin and in carbon fibre-epoxy laminate forms. Room temperature fracture and yield behaviour of highly cross linked and rubber modified methacrylates, of rubber modified dysfunctional epoxies, as well as of the above mentioned epoxy/polyether sulphone blends, is investigated. Special emphasis is placed on a comparison of the kinetics of tensile creep between the different systems. Loss of ductility in the highly cross linked resins is shown to result in a very limited scope for toughness enhancement by the usual rubber toughening methods.